The 3GPP has agreed certain principals for the transmission of system information over the air in future cellular communications networks, such as their so-called Long Term Evolution (LTE) networks. These principals include:                System information (SI) is broadcast in each cell (or base station) and any UE that wants to access the service of the system needs to read the SI;        A fixed amount of some key SI is to be sent on the broadcast transport channel (BCH);        For the remaining SI, SI that has the same scheduling requirements (i.e. periodicity) is grouped into a scheduling unit (SU) and that is sent using downlink shared transport channel (DL-SCH). There can be multiple scheduling units which may contain a variable amount of SI. The most frequently sent SI is grouped into a scheduling unit called SU-1.        The BCH contains scheduling information relating to SU-1 (i.e. when SU-1 is sent), and SU-1 contains scheduling information relating to other SU.        UE needs to acquire SI on BCH and SI in SU-1 on DL-SCH at least for cell selection and reselection;        The 3GPP has also specified coverage and performance requirement for the BCH to be 98% coverage with 1% BLER. The same coverage and performance is required for the DL-SCH carrying SU-1.        
In general, the DL-SCH carries payload from the higher layer (L2 data) which can be SU or other traffic or control information. DL-SCH has a number of transmission properties or transmission configurations that the system can control to effectively deliver the data from BTS to the UE. 3GPP agreed that at least the following transmission configurations are under control of the network:                Resource assignment for DL-SCH: i.e. how many virtual or physical resource blocks are used for the DL-SCH and their location in the system bandwidth;        the modulation scheme used for DL-SCH: e.g. either QPSK or 16 QAM or 64 QAM;        the transport block size (or payload size) information of the DL-SCH: this information together with number of assigned RB and modulation scheme indicates the transport block size;        HARQ information for the DL-SCH.        M1MO related information        
For each DL-SCH, there is a need to transmit an associated L1/L2 control channel which contains transmission configurations of the DL-SCH so that UE can receive and decode DL-SCH correctly. The transmission configurations of the L1/L2 control channel are known to the UE so that UE can receive it. The CRC bits of L1/L2 control channel are masked by some ID that only one UE that knows the ID can decode the L1/L2 control information correctly and then decode the DL-SCH. If a common ID is used then all UE sharing the same ID could decode L1/L2 control information and then decode the DL-SCH. So by varying the ID information e.g. making it common to many UE or unique to one UE, the system can use the DL-SCH for transmitting a common or dedicated logical channel respectively.
As noted above, when DL-SCH carries SU-1, the same coverage and performance requirement (98% coverage with 1% BLER) is applicable for its associated L1/L2 control channel. An exemplary estimation of the physical resource overhead required for transmission of such L1/L2 control channel is given below.
As an example, in the case of 5 MHz system, the total L1/L2 control information will be about 40 bits including the 16 bits CRC. Some preliminary evaluation by the 3GPP has shown that to achieve 98% coverage and 1% BLER, the coding rate has to be about 1/12 for two transmission antennas and 1/24 for one transmission antenna. Therefore, for the 40 bit payload specified above, the physical resource overhead required is 480 bits and 960 bits i.e. 240 and 480 RE, respectively, for the two antenna and one antenna cases, when QPSK modulation is used. The maximum physical resource available for transmission of all L1/L2 control channels is 800 and 850 RE for the two antenna and one antenna cases respectively, making the physical resource overhead for this L1/L2 control 30% and 56%, respectively.
Accordingly it is desirable to reduce the level of overhead for this L1/L2 control channel in such systems.